The Duke of Edinburgh has reportedly said in a private conversation with the director of a windfarm company that wind turbines "never work", that they are reliant on government subsidies and that their supporters believe in "fairytales". The Sunday Telegraph reported:

The Duke of Edinburgh has made a fierce attack on wind farms, describing them as "absolutely useless". In a withering assault on the onshore wind turbine industry, the Duke said the farms were "a disgrace".

He also criticised the industry's reliance on subsidies from electricity customers, claimed wind farms would "never work" and accused people who support them of believing in a "fairy tale".

When Esbjorn Wilmar, of Infinergy, which builds and operates turbines, introduced himself to the Duke at a reception in London, he found himself on the end of an outspoken attack on his industry.

"He said they were absolutely useless, completely reliant on subsidies and an absolute disgrace," said Mr Wilmar. "I was surprised by his very frank views." Mr Wilmar said his attempts to argue that onshore wind farms were one of the most cost-effective forms of renewable energy received a fierce response from the Duke.

"He said, 'You don't believe in fairy tales do you?'" said Mr Wilmar. "He said that they would never work as they need back-up capacity."

Are windfarms useless? Are they as efficient as other energy sources? Are they completely reliant on subsidies?

I'm going to try and round-up the most independent research available on this to answer these questions. Do you have any evidence that could help? Get in touch below the line, email me at polly.curtis@guardian.co.uk or tweet @pollycurtis

Analysis

I've started off by speaking with Professor Jim Skea, research director of the UK Energy Research Centre (UKERC) and a member of the government's independent Committee on Climate Change. The UKERC is an academic group with government funding that was established to provide independent scientific advice on sustainable energy systems. He told me:

The arguments against windfarms are: they are ugly, they don't work and they need subsidies. In terms of the aesthetics, it's a matter of taste. Some people like them, some don't. There's nothing scientific to say about that. On the "they don't work" issue, it's quite clear that they do generate electricity. If you look at the machinery they are getting nearly 30% compared to their peak capacity [the load factor]. There is a limited degree of predictability about the wind so they do need to be backed up. But not as much as people think because the law of statistics means that the wind is likely to be blowing somewhere.

The UK has one of the best wind resources in Europe. Far better than Germany. Going off-shore the wind resource is even better – with load factors up to 40%. If you are going to capture energy from wind it's as good as you're going to get. It's just a question of whether you think it's worth it. We as researchers say this is the best guess of the costs; it is a political choice whether you want to pay for it.

Winds-farms are being subsidised. For onshore wind, subsidies are going down compared with the cost of gas which is going up. If you include the carbon costs, in the future you can see a point where there is parity between non-renewable and wind energy. Perhaps by 2020. In Texas they have got parity. Some of the best wind turbines in the UK can do that already.

The other point is the question of offshore – it is more expensive than onshore because you have to connect and get it onshore. They are being subsidised more heavily. There are prospects of getting the costs down but it will be well into the 2020s before that happens. The reason windfarms are going offshore is because it is harder to get planning permission.

I've also been canvassing the opinions of colleagues at the Guardian who write regularly on this subject.

James Randerson, the Guardian's environment and science news editor, expands on Prof Skea's point above about the "load factor" - the efficiency of turbines measured as a ratio from their average production compared with their peak production and how fluctuations in the weather are managed, known in the industry jargon as "intermittencey". This is the "back-up" capacity that Prince Philip says is the reason that windfarms "Never work". He writes:

The argument centres around back up power for when the wind is not blowing. That comes from fossil fuel plants and the charge is that the act of ramping up and then damping down the output of those plants in response to fluctuations in the wind makes those plants less efficient and therefore more carbon intensive. So opponents of wind say that any benefit from the reduced carbon emissions from wind is counter-balanced by the reduced efficiency of the coal and gas plants. In fact, that loss in efficiency appears to be small by comparison.

There's a good summary here that includes some real data on what happened when Colorado increased wind from 2.5% of electricity to 6.1%.

Also, there is something else at play which improves the carbon-cutting credentials of wind. In order to respond to the ups and downs of wind, power grids tend to move more to relying on more flexible gas plants then coal - which is also more carbon intensive.

What is clear is that to make the most of renewables you need lots of connectivity in the grid. Hence the move to improve connections across Europe - ie the creation of a so-called super-grid.

The question of intermittency is central to the wind-farm debate. The UKERC reported on the issue in 2006 here. It reported:

It is sometimes said that wind energy,for example,does not reduce carbon dioxide emissions because the intermittent nature of its output means it needs to be backed up by fossil fuel plant. Wind turbines do not displace fossil generating capacityon a one-for-one basis. But it is unambiguously the case that wind energy can displace fossil fuel-based generation,reducing both fuel use and carbon dioxide emissions.

It goes on:

System balancing entails costs which are passed on to electricity consumers. Intermittent generation adds to these costs. For penetrations of intermittent renewables up to 20% of electricity supply,additional system balancing reserves due to short term (hourly) fluctuations in wind generation amount to about 5-10% of installed wind capacity. Globally,most studies estimate that the associated costs are less than £5/MWh of intermittent output,in some cases substantially less. The range in UK relevant studies is £2 - £3/MWh.

It concludes that:

Additional conventional capacity to maintain system reliability during demand peaks amounts to around 15% to 22% of installed intermittent capacity.

It's clear that back-up requirements do reduce the efficiency of windfarms - the UKERC study from 2006 suggested by about 15-22%. But the amount of back-up required does not cancel out the amount of electricity windfarms produce.

I'm going to look now at the relative costs of on and off-shore wind-farms and the impact of the subsidies. Do you have any relevant evidence? Get in touch below the line, email me at polly.curtis@guardian.co.uk or tweet @pollycurtis

In this report from last year the UKERC looks at the cost of offshore windfarms, which are more technically efficient than onshore farms once built because of the better weather conditions at sea. But as Prof Skea points out above, they are more expensive to build and this report finds that the cost of building them has doubled in five years.

Onshore wind has recently been estimated to be the lowest cost large scale, commercially available low carbon generator applicable in the UK. In contrast, offshore wind is the most expensive... Whilst some commentators remain optimistic and see the potential for creating significant economic benefit from offshore wind development, others anticipate a relatively high cost future for UK offshore wind, at least in the short to medium term.

It also points out that the costs are high because the technology is still new – and that in the same period the price of fossil fuels has also increased.

It is important not to lose sight of the fact that offshore wind is still in its infancy– in terms of energy output we are still building the equivalent of the UK's first conventional power station. So-called 'first of a kind' costs still apply in large part to offshore wind.

On this point, Damian Carrington, the head of environment for the Guardian, argues that all technologies are subsidised when they are new.

All new energy technologies have received subsidies in their early years, as governments see their development as a public good. In this case, renewables cut the emissions causing climate change and protect the nation against energy insecurity. The difference with renewables over fossil fuels and nuclear power is that the past and current subsidies going to the unsustainable sectors is far, far bigger. In 2010, fossil fuels were subsidised to the tune of $409bn globally, while renewables got $66bn.

Damian has also highlighted new research suggesting that wind power could break even with non-renewable energy sources as soon as 2015.

The average wind farm will produce electricity as economically as coal, gas and nuclear power stations by within five years. That - a statement blowing the argument that wind power is too expensive to pieces - comes not from campaigners but from the hard-headed financial analysts at Bloomberg. They say the best wind farms in the world already match their fossil fuel rivals.

1.28pm: Below the line @spike25 responded to @somemightsay's query about the carbon footprint of windfarms by posting this research conducted by the scientific research unit in Parliament. It concludes:

Electricity generated from wind energy has one of the lowest carbon footprints. As with other low carbon technologies, nearly all the emissions occur during the manufacturing and construction phases, arising from the production of steel for the tower, concrete for the foundations and epoxy/fibreglass for the rotor blades.10 These account for 98% of the total life cycle CO2 emissions. Emissions generated during operation of wind turbines arise from routine maintenance inspection trips. This includes use of lubricants and transport. Onshore wind turbines are accessed by vehicle, while offshore turbines are maintained using boats and helicopters. The manufacturing process for both onshore and offshore wind plant is very similar, so life cycle assessment shows that there is little difference between the carbon footprint of onshore (4.64gCO2eq/kWh) versus offshore (5.25gCO2eq/kWh) wind generation (Fig 2).11 The footprint of an offshore turbine is marginally greater because it requires larger foundations.

The Centre for Sustainable Energy, which is a green group campaigning for more sustainable energy, has compiled this interesting report addressing common concerns about wind power. The group clearly has a green agenda but the report is based on peer-reviewed academic studies. It addresses a lot of the local issues that arise with a windfarm – public acceptance, property prices, safety, noise and bat and bird mortality.

On windfarms' carbon footprint it says that wind compares "favourably" with other energy production methods and on intermittency it concludes:

The unreliability of wind as an energy source has been overestimated and suppliers are used to dealing with changes in supply and demand.

Thanks @somemightsay for raising the issue and thanks @spike25 for coming up with such a solid source of information.

2.16pm:

I've finally got hold of the really interesting data I was looking for on the relative costs of different energy sources. The following three tables are from the UK Electricity Generation Costs Update conducted by the consultants Mott MacDonald for the government last year. You can read the full report here. (Many thanks to Adam Bell of RenewableUK for pointing me towards this information.)

The charts show the average cost for each megawatt hour of electricity produced by each energy source over the lifetime of the power station, windfarm or other generator producing it. The longer the lifetime of the plant the cheaper the cost becomes over time. The first, for projects starting in 2009 shows that gas is the cheapest fuel but that onshore wind is more cost efficient than all forms of coal and nuclear but that offshore wind is the most expensive. (FOAK stands for "first of a kind" and NOAK stands for 'nth of a kind".) By 2017 new projects will see onshore wind as the cheapest source raising the prospect that subsidies will even have to shift more towards non-renewable sources.

Levelised costs of main technologies for projects started in 2009. Source: Mott MacDonald.

Levelised costs of main technologies for projects started in 2013. Source: Mott MacDonald.

Levelised costs of main technologies for projects started in 2017. Source Mott MacDonald.

2.45pm:

This chart from Ofgem shows the costs of the government's green policies for the average dual fuel bill. It shows that 6% of the bill is down to environmental obligations. An Ofgem press office told me that if you take electricity alone then green subsidies cost a person with an average annual bill of £440 just £19 a year.

It's worth remembering that once installed those wind turbines do indeed provide "renewable" energy. They do not need refuelling at a future price unknown. They provide an element of local energy security that is hard to measure in financial term but could be worth a fortune strategically. Wind farms are not subject to the vagaries of Opec oil embargoes, Middle East wars or other issues that can drive up the price of oil and even cut supplies off completely. Neither does wind require companies to dig up carbon heavy tar sands or risk polluting the beaches of the US Gulf - never mind the pristine waters of the Arctic. The oil industry has never had to pay the price of its historic legacy: global warming and climate change. Ask the people of Tuvalu to draw up a bill for the potential loss of their country to carbon-induced rising sea levels. Wind needs subsidies to get going. Oil still needs them apparently - a century on. The UK government still has to give oil companies tax breaks to convince them to keep producing in the North Sea.

5.20pm:

Conclusion: Do windfarms work?

Windfarms produce electricity but currently at a higher cost to fossil fuels. However, over the longterm today's onshore windfarms will prove cheaper than coal and nuclear and those built from 2017, are predicted to be cheaper than gas as well (see 2.16pm).

Offshore windfarms are much more expensive to build and it will take longer for them to become cost effective (see 12.32pm). But they are more popular because they are less imposing on the populated landscape and produce moreenergy because of higher winds.

Windfarms will always require other sources of energy to cushion falls in production caused by changes in weather conditions and sudden surges in demand. Around 15% to 22% of electricity produced by wind power must be supplemented by other sources to cope with fluctuations. It still amounts to a net gain in energy and reduction in the need for carbon sources but it means the technology to some extent will always rely on traditional back-up. However, it requires no fuel to run a windfarm, unlike other non-renewable sources that are heavily dependent.

The Duke of Edinburgh is right that windfarms currently do require subsidies. All new energy sources require government subsidies to help them develop. The cost effectiveness of such subsidies depends on the political value you put on developing alternative clean sources of energy.

It's worth remembering that the government also subsidises some fossil fuels, such as through tax breaks to encourage north sea drilling for oil to continue (see 4.47pm). In 2010, fossil fuels were subsidised to the tune of $409bn globally, while renewables got $66bn. The subsidy for renewable energy sources on the average £440 electricity bill is currently £19.